Are there any accepted authorities of Halacha that permit a man to eat (i.e., "real" eating such as consuming cake or cereal) before davening Shacharis under "normal circumstances" (i.e., a healthy person with no other reason to eat then other than "they are hungry")?

@SethJ It does seem to be a tefilla issue not a keriat shema issue (cf Brachot 10b, and its placement among the laws of tefillah in the Rambam and Shulchan Aruch) so I don't see reason to distinguish.
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Double AA♦Sep 7 '12 at 9:05

It says in Hayom Yom for Yud Shvat that when Rebbetzin Rivka (who was the wife of the Rebbe Maharash, the fourth Lubavitcher Rebbe) was eighteenth she felt ill. The doctors told her that she must eat breakfast. She didn't want to eat before Davening so she started Davening early and afterwards eating breakfast [I assume that means that by her normal wake-up time she was already finished davening and could eat].

Her father-in-law (The Tzemach Tzedek of Lubavitch) said "A Jew must be healthy and strong..." He then said "You should not be without food. It's better to eat for the sake of davening than to daven for the sake of eating".

In general, in chabad one learns chassidus before davening which results in shacharis starting 9:00-10:00. Therefore, the custom in Chabad is to eat before davening and in most (if not all) chabad yeshivas, mzonos is commonly served before davening.